The objective of this work was to evaluate the production (number and weight) and composition (contents of lipid, protein, carbohydrate and ashes) of Euphorbia heterophyllaseeds (susceptible and resistant biotypes to ALS-inhibiting herbicides), Bidens pilosa and Desmodium tortuosum under field conditions. Biotypes of E. heterophylla presented the highest weight of 100 seeds. D. tortuosum produced the largest number of seeds per plant (714.25). For all the evaluated species, most of the seed dry biomass reserve was constituted of carbohydrate with B. pilosa presenting the largest accumulation (61.7%). Biotypes of E. heterophylla accumulated higher amounts of lipids and ashes, while D. tortuosum accumulated higher protein content (34.8%). Biotypes of E. heterophylla did not differ in their seed production and composition.